Adolescents are expected to chafe at adult oversight, act impulsively and brood about the meaning of life.

But adolescents who were adopted in infancy are almost twice as likely as their non-adopted peers to end up in counseling for those kinds of behaviors, a fact that leaves many adoptive parents wondering: Do adopted children really have more adjustment problems in adolescence? Or do adoptive parents, hypervigilant as they famously are, overreact to the conventional struggles of young adulthood and refer their children to mental health professionals more often than need be?

Now research involving more than 1,000 adolescents is helping to settle those long-standing questions.

The work supports previous indications that, as a group, adopted adolescents really are more likely to wrestle with behavioral and mental health issues than those who are raised by their biological parents, exhibiting higher rates of attention-deficit hyperactivity disorder (ADHD) in particular.

But the new study also suggests that, for reasons that remain largely mysterious, those risks vary considerably, with children adopted from foreign lands adjusting considerably better, on average, than those adopted domestically.

Gratifyingly, the analysis also confirms that the vast majority of adoptees navigate the roiling waters of adolescence just as skillfully as their non-adopted friends and classmates.

"Adoption is a very emotional and politicized area," said Matthew McGue, a professor of psychology at the University of Minnesota, who led the study. "So it's important to recognize and emphasize that most of these kids are doing fine."

Adoption has been going on for a long time (think Moses, after all), and the extended family of adopted children grows bigger all the time. Last year, about 120,000 children were adopted in the United States alone, and U.S. adoptees younger than 18 now number about 1.5 million.

Although adoption has given most of those children spectacular opportunities, it is not surprising that at least some of them might have especially tough times during adolescence. By its nature, adoption raises in children precisely the kinds of doubts and insecurities already associated with that fast-changing time of life, including questions about personal identity, the meaning of family and the fine line between independence and abandonment.

That overlap has complicated efforts to disentangle the mental health issues specific to adopted adolescents, just as the lack of family history for many adoptees sometimes complicates medical diagnoses later in life.

Such complexities have only increased with the growth in international adoptions in the past few decades. Worldwide, about 40,000 children are adopted across national borders every year, through a network that encompasses more than 100 countries. In the United States, nearly a quarter-million children from overseas have been adopted in the past 20 years.

Bearing racial and ethnic traits clearly different from those of the parents who raise them, these children have little choice but to have their status as adoptees known to all before they themselves have begun to sort out the meaning of their situation, in many cases rushing their consideration of who they are, where they came from and why they were given up for adoption.